Present invention relates to hydraulic systems and, more particularly, to hydraulic systems including individually controlled spool valves coupled with respective actuators.
In a work machine such as bulldozer, excavator or the like, multiple hydraulic stacks may be provided for operation of multiple different hydraulic loads such as hydraulic cylinders for different functions. Each hydraulic stack is typically separately controlled using a plurality of valves which direct flow depending upon pressure differentials, or positively controlled using electrical or mechanical actuators.
It is known to provide a hydraulic system with multiple hydraulic stacks, with each stack having a meter-in spool valve and a meter-out spool valve for controlling hydraulic flow to an actuator, as well as controlling hydraulic flow from the actuator to a tank and providing make-up and line relief function. Load hold check valve should be positioned within a fluid line feeding each of the hydraulic stacks in parallel. Regeneration of hydraulic oil from one hydraulic stack to another cannot be achieved since the load hold check valve remains closed except when the pressure from the pump exceeds the pressure within the parallel fluid lines leading to each hydraulic stack. Moreover, the meter-out spool-type valve may be relatively costly and bulky.
Example of a hydraulic system which may be utilized with a work machine as described above is disclosed in U.S. Pat. No. 4,250,794 (Haak et al.), which is assigned to the assignee of the present invention. Haak et al. discloses the hydraulic system including a load hold check valve with a pressure control chamber which is fluidly coupled with a two position, two-way valve for the purpose of opening and closing the load hold check valve for supplying pressurized oil to an actuator.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, the hydraulic system provided with the hydraulic pressure source and at least one meter-in spool valve. Each Spool valve has an inlet and an outlet. A hydraulic actuator is fluidly coupled with the spool valve outlet. A load hold check valve fluidly interconnects the pressure source with at least one spool valve inlet. The load hold check valve has a pressure control chamber. A three way valve has a first port in fluid communication with the pressure control chamber, a second port in fluid communication with at least one spool valve inlet, and a third port in fluid communication with the pressure source.
In another aspect of the invention, a hydraulic system is provided with a hydraulic pump and at least one meter-in spool valve. Each spool valve has an inlet and an outlet. At least one hydraulic actuator is provided, with each hydraulic actuator being fluidly coupled with a corresponding spool valve outlet. A load hold check valve fluidly interconnects the pump with each spool valve inlet. A tank and at least one poppet valve assembly are also provided. Each poppet valve assembly is fluidly connected with a corresponding spool valve outlet and actuator. Each poppet valve assembly selectively interconnects corresponding actuator with the tank or an ambient pressure.